Journalists for Democracy in Sri Lanka, which obtained the material, said it was filmed in January 2009 – when the international media were prevented by the Sri Lankan government from covering the conflict zone.

The Sri Lankan High Commission denied the government had carried out atrocities against the Tamil community. A Sri Lankan army spokesman also called the video a “fake”.

“What makes the video credible is that telltale casual dialogue between the killers as they dispatch their helpless captives.”Jonathan Miller

“While it’s true that Tamil Tiger insurgents were known to masquerade in government uniforms, what makes the video credible is that telltale casual dialogue between the killers as they dispatch their helpless captives,” explains Foreign Correspondent Jonathan Miller.

For Sri Lanka’s Sinhalese majority, the end of 26 years of war was something to celebrate; the rebel Tamil Tiger army vanquished. It had been a brutal war with upwards of 80,000 dead and soldiers, civilians, Sinhalese and Tamil traumatised and brutalised by what they has been through.

By January 2009, government forces were closing in on a shrinking conflict zone with unknown thousands of Tamil civilians being killed.

Independent journalists and observers were prevented from getting anywhere near the combat. There were rumours terrible things were happening, but this was a war without witnesses.

However one soldier apparently had a mobile phone. Eight months after it was filmed, his footage of a callous execution was broadcast by Channel 4 News. There is no indication of the ethnicity of the dead men, but the group which obtained the pictures claim the victims are Tamils.

Blog: investigating claims of war crimes"The casual banter and laughter of the uniformed killers was what I immediately found so callous and shocking, as they kicked in the head and then shot - point-blank - their bound, blindfolded, naked victims.

"The raw footage - one continuous shot lasting one minute and eight seconds - is sickening.

"While it's true that Tamil Tiger insurgents were known to masquerade in government uniforms, what makes the video credible is that telltale casual dialogue between the killers as they dispatch their helpless captives."

A naked man is seen; blindfolded and bound, his last human contact, a kick in the head. “It’s like he jumped,” a soldier laughs.

His Sinhalese accent is of a country boy. His tone is casual, like this was a game.

As further gunshots ring out, the camera pans to reveal other bound bodies – eight in total, and all but one naked.

There is no indication of the ethnicity of the dead men, but the group which obtained the pictures claim the victims are Tamils. The killers are speaking Sinhala; they are wearing what appear to be Sri Lankan Army uniforms.

Towards the end of the video, a ninth man is shot dead.

Extra-judicial killings by government soldiers and paramilitaries have been documented for years in Sri Lanka, but there had never been evidence like this video before.

It is impossible to independently authenticate the pictures. The group of exiled Sri Lankan journalists who passed the footage to Channel 4 News are not a Tamil liberation group: they campaign for press freedom.

The existence of such footage had been rumoured for months; these pictures were reportedly filmed in January 2009, but only smuggled out of Sri Lanka two days before Channel 4 News broadcast them. A Sinhalese human rights investigator who watched the material on the day it was broadcast believed it to be genuine.

Sri Lanka High Commission statement

"The High Commission of Sri Lanka categorically deny that the Sri Lankan armed forces engaged in atrocities against Sri Lankan Tamil community. They were only engaged in a military offensive against the LTTE.

"The High Commission has noted that in many instances in the past, various media institutions used doctored videos, photographs and documents to defame the Sri Lankan government and armed forces.

"Therefore, we request you to verify the authenticity of the video footage before the telecast."

Sri Lankan army spokesman Brigadier Udaya Nanayakkara said the footage was a fabrication designed to discredit security forces.

He said: “This video has been made to discredit the armed forces. This was said to have been filmed at a time when the Tigers too were operating dressed in Sri Lankan military uniforms.”